The present invention relates to a stator for electric machines, especially machines of the kind constructed with separately wound poles and with yoke components required between these poles for the magnetic flux. The invention also comprises a method for the production of the stator in question.
A large number of motor variants, e.g. commutator motors and shaded pole motors, are provided with stators as specified above. These motors are generally designed for high speeds, have small or medium ratings, and are used for, for instance, fans, blowers, vacuum cleaners and similar appliances. However, these motors have certain serious disadvantages. Their dimensions are large and they are heavy. This is partly on account of the collector system required for certain types of motor but it is also because of the solid and cumbersome pair of poles. The stators have mechanically weak sectors which impede the accurate centering of the rotor system and entail considerable air gap requirements with resultant poor efficiency. The very poor efficiency produces great thermal losses which directly preclude the construction of larger units. The overall picture is of windings that are very compact, surrounded to a very great extent by large masses of sheet metal and consequently have small surfaces for thermal radiation. The stators of these motors are made of laminations stacked at an angle of 90.degree. to the longitudinal axis of the rotor. The lamination sections are of a complex nature and this incurs a great deal of material wastage and expensive joining of the laminations.
A typical example of this technique is the 2-pole commutator motor illustrated in FIG. 1, which shows an end view and a partial section through the motor, the two salient poles 1 and 2 of which are connected by the yoke components 3 and 4. The two poles are encircled by the windings 5 and 6 respectively. The current through the windings generates a magnetic flux 7, which passes from pole 1 through the rotor 8 to pole 2. The magnetic circuit is closed by the return flux in the two yoke components 3 and 4. The sectional areas of these yoke components are accordingly dimensioned to allow the passage of the total flux. A certain pole width, indicated by the numeral 9, is required to run the motor. This width gives the pole a sectional area which is many times that of the yoke components 3 and 4. Consequently the flux density in the poles will be considerably lower than in the yoke components, and certain parts of the salient poles, for instance that indicated by the numeral 10, have slight or zero magnetic flux. The motors as described above always have proportionally very considerable core losses. In addition there is very little possibility of cooling as the windings are almost completely encircled by the masses of iron, yokes and poles. This, together with the core losses, presents serious problems with regard to the cooling of motors of this type.
In order to overcome these deficiences proposals (U.S. Pat. Nos. 2,449,021 and 3,591,819) have previously been made for arranging the stator laminations in the longitudinal direction of the rotor and bending the edges of the laminations in towards the stator bore. Since the magnetic flux into the stator bore will then be entirely determined by the relative positions of the laminations edges, serious problems have been encountered instead in aligning these edges. One way of solving these problems has been to bend the extreme outer part of the edge to form a 90.degree. angle with the laminations and accordingly let the outer ends of the laminations abut each other. Another solution has been to secure special fixtures to the edges of the laminations in order to determine their relative positions. Both of these proposed solutions produce an inaccurate circular-shaped stator bore and it has not proved possible to machine this bore by turning or other similar methods. Apart from the inaccuracy of form of the stator bore the production of these devices is expensive as well. One way to reduce the costs has been to divide the laminations and produce stacks that can be slid into each other. Such an arrangement, however, produces heavy losses as the magnetic flux has to pass an air gap.